This invention relates to a plastic pallet assembly for storing or transporting goods.
Pallets used in industry today are most commonly formed of wood slats and stringers or blocks which are nailed together. While such pallets are functional, they have many disadvantages. First, wood pallets are relatively heavy. Second, wood is not easily cleaned because it absorbs water and other liquids which damage and warp the wood. For these same reasons, the use of wood pallets outside or in wet environments is also limited. Wood pallets are often not consistently dimensioned due to size variations in the wood slats and shrinkage of wood over time, thus preventing such pallets from being stacked or stored in a stable or consistent manner. Also, inconsistent dimensions make automation of these pallets more difficult. Further, the nails used to fasten wood pallets together may cause damage to goods which are stored and transported on the pallet, or wood splinter may result after time. Moreover, once wood pallets are damaged, they have little or no residual value and also necessitate disposal fees.
Replacing wood pallets with plastic pallets has been a goal for many years. The advantages of plastic pallets are many as compared to wood, including greater durability, lighter weight, more consistent dimensions, improved cleanliness, water resistance, higher residual value for recycling, and no nails which may damage products being supported thereon. While many plastic pallets have been attempted, the designs that are able to approximate the strength of wood, to date, have been cost prohibitive and may not have the requisite strength properties. For example, plastic pallets having a solid section, while having favorable stiffness and deflection properties, are heavy and utilize a relatively large quantity of material in their formation. Wood is five to eight times stiffer than a typical plastic used to make pallets. Plastic pallets must either use much more material, be taller, or have reinforcements such as steel rods or glass fillers to compensate for this difference. While conventional plastic pallets have ribbed supports to decrease their weight, they often lack the desired stiffness and low creep properties of the solid pallet, and in order to improve these properties, the height of the pallet must be increased, or reinforcements must be added to the plastic such as steel or other composite reinforcements. Of course, these additions to the plastic cause an increase in material density leading to an even heavier pallet. Further, engineering resins are very expensive resulting in a more expensive pallet.
Another hurdle to overcome with plastic is the cost. Plastic pallets are more expensive than wood by three to five times. This cost can be offset by the number of trips or shipments that can be achieved with plastic versus wood pallets. Another major hurdle is the stiffness of plastic pallets. Racking loaded pallets in warehouses for upwards of 30 days may be common, and the combination of low tensile strength and creep may limit the use of plastic in this manner.
There are three conventional methods of overcoming these weaknesses. The first is to add reinforcement such as steel or a composite to the pallet. This generally adds significant cost and weight and complicates recycling of the pallet. The second is to make the pallet taller. This generally limits the height of a product which is to be stacked on the pallet, as well as the number of pallets that may be stored in a given area. The third is to use reinforced or engineered resins. Again, this adds significant cost and weight. All three obviously limit the acceptance of plastic pallets.
U.S. Pat. No. 3,580,190 provides a partial solution to the stiffness problem by attaching top and bottom sheets 22,24 to the structural network 23, as shown in FIG. 1 thereof. However, this solution does not resolve the bending stiffness problem because large lateral and longitudinal unsupported areas still exist, such as in areas 26, 37, 38, 49 and 50. In other words, this design merely further stiffens the support column areas 67, 68, 69, 97, 98, 99, 28, 30, 32, which already provide substantial stiffness merely as a result of their height. The weakness of this design is apparent in column 6, lines 60-71, where the reference recommends the use of a material having a flexural modulus (or Young""s modulus) greater than about 200,000 psi. Such a high modulus material is apparently required because the structure described does not provide significant resistance to deflection along the length and width of the pallet. High modulus materials add substantial cost to the pallet.
Moreover, pallets typically require large openings for receipt of pallet jacks. Because of these large openings, the pallet structure is typically thin and weak and has poor deflection stiffness. Because pallets are exposed to significant abuse, any solution to the stiffness problem must not adversely affect the impact strength of the pallet.
Consequently, an improved pallet is desired which should be reasonably inexpensive, lightweight and sturdy. The improved pallet should also have improved stiffness and creep properties. The pallet should also be able to withstand various environmental conditions to which it may be exposed, particularly moisture. The improved pallet should also be easy to store, have a size compatible with a standard wood pallet, and be reusable. Also, a need exists for improving the stiffness of plastic pallets configured to receive a pallet jack, without reducing impact strength of the pallet. The improved pallet design should also apply to components used in association with pallets.
It is a principal object according to the present invention to provide an improved pallet assembly which is relatively lightweight, inexpensive to manufacture and assemble, and consistently dimensioned.
It is another object according to the present invention to provide an improved pallet assembly which has desirable strength, stiffness, creep, and deflection properties.
It is another object according to the present invention to provide an improved pallet assembly which is able to withstand varied environmental conditions, particularly moisture, with little damage or wear and is readily reusable.
It is yet another object according to the present invention to provide an improved pallet assembly which may be stored, racked or stacked in a stable manner.
Another object of the present invention is to provide a method of structurally reinforcing a plastic pallet configured to receive a pallet jack, in a manner which improves stiffness without loss of impact strength.
It is yet another object to provide a highly stiff pallet without the use of the reinforcements or engineered resins which increase the cost and weight of the pallet, i.e., to provide an inherently stiff pallet design.
Further, it is another object according to the present invention to provide an improved design for components used in association with pallets, such as a pallet top frame.
In carrying out these and other objects and goals according to the present invention, a pallet assembly is provided which includes a top deck formed of plastic which has a first opposing surface having a plurality of first flanged portions projecting downwardly therefrom. The pallet assembly top deck portion has a substantially planar upper surface upon which a plurality of objects may be rested. The pallet assembly also includes a bottom deck portion which is also formed of plastic and has a second opposing surface with a plurality of second flanged portions projecting therefrom in an upward direction. In this assembly, the pluralities of second flanged portions correspond to and securely mate with the plurality of first flanged portions to define a plurality of columns between the top deck and bottom deck portions, said top and bottom deck portions and said columns having a box beam cross-section for providing strength to the pallet assembly.
The overall box beam pallet design according to the present invention also has desirable improved properties, such as increased stiffness versus weight, over other standard beam section designs having equivalent surface areas, sizes, and weights, such as a T-rib beam, or an inverted-U (multiple ribbed) design, and has properties equivalent to that of the I-beam section.
In a preferred assembly, the top deck portion includes a top member and a mid-top member which have corresponding mating flanged surfaces which are securely mated to each other. In this preferred assembly, the mid-top member has the first opposing surface opposite the corresponding mating flanged surfaces. In still another preferred assembly, the bottom deck portion includes a bottom member and a mid-bottom member each having corresponding mating flanged surfaces which are securely mated to each other. In this preferred assembly, the mid-bottom member has the second opposing surface opposite its corresponding mating flange surfaces.
More particularly, the first or top member includes a substantially flat top surface with ribs protruding in a downward direction. The second or mid-top member has a substantially flat bottom surface with ribs extending in an upward direction and partial support columns extending down from this surface. The ribs on both these parts are aligned so they can be welded together by plasticizing their mating surfaces preferably via a hot-plate welding operation to form a box beam top deck. The third or mid-bottom member has a substantially flat upper surface with ribs extending down and partial columns extending up. The fourth or bottom member has a substantially flat bottom surface with ribs extending up. Again, the ribs on both parts are aligned so they can be welded together in a second hot plate welding operation to form a box beam bottom deck. Lastly, the box beam top deck and box beam bottom deck are welded together at the columns that also align, resulting in a pallet where every section is a box beam. In the preferred embodiment, each boxed section has a perforated top and bottom to allow for cleaning and drainage. These perforations may easily be eliminated to create true boxed sections.
In a second embodiment according to the present invention, there is provided a plastic pallet assembly which includes a first pallet portion which is formed of plastic and has a first opposed surface having a plurality of first spacer portions projecting downwardly therefrom which define a first matching surface. This second embodiment also includes a second pallet portion which is also formed of plastic and has a second opposed surface having a plurality of second spacer portions projecting upwardly therefrom which define a second matching surface. The plurality of first and second matching surfaces are then heated to a plasticized state, compressed together, and subsequently cooled in order to define a plurality of columns for spacing apart the first pallet portion and the second pallet portion, each column, first and second pallet portions each having a box beam cross-section for providing strength to the pallet assembly. This method is preferably performed via hot plate welding. In a preferred version of this second embodiment, the first pallet portion includes a first outer member and a first inner member having opposing surfaces which are securely attached to each other by heating them to a plasticized state, compressing them together, and cooling them. As in the first embodiment, the first outer member has a substantially planar first outer surface for supporting and transporting one or more objects thereupon.
Further, the second pallet portion may include a second outer member and a second inner member which have opposing surfaces securely mounted to each other by the process of heating the opposing surfaces to a plasticized state, compressing them together, and cooling them.
In a third embodiment according to the present invention, a plastic pallet assembly includes a first pallet portion which is formed of plastic and includes a top member and a top intermediate member (mid-top member). Each of these members has a first pair of substantially planar surfaces spaced apart from the other and each further has a first pair of mating surfaces which are heat welded together in order to integrally define the first pallet portion. The third embodiment of the plastic pallet assembly also includes a second pallet portion which is formed of plastic and includes a bottom member and a bottom intermediate member (mid-bottom member), each having a second pair of substantially planar surfaces spaced apart from the other and each further having a second pair of mating surfaces which are heat welded together in order to integrally define the second pallet portion. The first intermediate member of the first pallet portion and the second intermediate member of the second pallet portion each has corresponding opposed mating edges which are heat welded together in order to integrally define the pallet assembly.
A fourth embodiment of the pallet assembly according to the present invention is formed substantially of plastic. The fourth embodiment includes a first outer member and a first intermediate member which are spaced apart from each other by a first pair of opposed mating surfaces extending therebetween. The opposed mating surfaces are integrally mounted to each other in order to define a first pallet portion. The fourth embodiment also includes a second outer member and a second intermediate member which are spaced apart from each other by a second pair of opposed mating surfaces extending therebetween. The second pair of opposed mating surfaces is integrally mounted to each other in order to define a second pallet portion. The second intermediate member is oriented adjacent the first intermediate member. The first intermediate member and the second intermediate member have corresponding mounting edge s projecting therefrom which are integrally mounted to each other in order to integrally define the pallet assembly. In this embodiment, the first outer member includes a lower surface with edges projecting therefrom which defines a one of the first pair of opposed mating surfaces, and the first intermediate member has an upper surface with corresponding edges projecting therefrom which defines an other of the first pair of opposed mating surfaces. The second outer member includes an upper surface with edges projecting therefrom which defines a one of the second pair of opposed mating surfaces, and the second intermediate member has a lower surface with corresponding edges projecting therefrom which defines an other of the second pair of opposed mating surfaces.
A fifth embodiment of the portable pallet assembly according to the present invention is for storing and transporting objects thereon and includes a first member which has a substantially planar first upper surface upon which the objects are placed, and also includes a first lower surface. This fifth embodiment also includes a second member which has a second upper surface and a second lower surface, where the second upper surface is securely mounted to the first lower surface to form a plurality of box beam cross-sections. The fifth embodiment further includes a third member which has a third upper surface and a third lower surface. The third upper surface and the second lower surface have corresponding flanged surfaces which are securely mounted to each other to in order to form a plurality of columns having box beam cross-sections defined thereby. This embodiment also includes a fourth member which has a fourth upper surface for mating with the third lower surface and also has a substantially planar fourth lower surface. The fourth upper surface is securely mounted to the third lower surface to form a plurality of box beam sections.
In a preferred version of this fifth embodiment, the second upper surface and first lower surface are each securely mounted to each other by introducing heat therebetween, plasticizing each surface, compressing the surfaces together, and allowing them to cool. In another preferred version, the fourth upper surface and third lower surface are securely mounted to each other by introducing heat therebetween, plasticizing each surface, compressing the surfaces together, and allowing them to cool.
Also disclosed according to the teachings of the present invention is a top frame for a pallet. A top frame is typically used in connection with the mass shipping of objects, such as empty bottles. The top frame is used to help stabilize the shipment of objects at the upper end in conjunction with a pallet at the lower end.
In keeping with the teachings of the present invention, a method for forming a pallet and a top frame for a pallet includes providing first and second pallet portions, each having corresponding mating flanged surfaces. The method also includes introducing heat to the corresponding mating flanged surfaces to melt the mating flanged surfaces in order to thereby form plasticized surfaces. The plasticized surfaces may then be pressed together, and then cooled to form a welded joint therebetween defining a plurality of box sections by the mating flanged surfaces. In this method, the step of providing a first and second pallet portions includes mounting and aligning them in a holding fixture. The step of introducing heat may include introducing a heated platen therebetween. Also, the method may also include the steps of retracting the heated platen from between the corresponding mating flanged surfaces prior to pressing them together and also opening the holding fixture and removing the welded pallet assembly at or near the end of the forming operation. The method may further include heating the mating flanged surfaces under pressure by contacting the heated platen to the mating flanged surfaces for melting the same.
In another method embodiment, more specifically, the present invention provides a method of reinforcing a plastic pallet having a thin top deck portion, a plurality of support columns extending from the top deck portion and a plurality of support rails connected to the support columns to form a thin bottom deck portion, wherein the support rails each include a sheet portion with a plurality of vertical ribs extending therefrom. The method includes the step of welding a plurality of plastic sheets to the vertical ribs between the support columns to form a plurality of substantially rectangular hollow vertical cross-sections along the length of the support rails for improved stiffness. It is contemplated that the substantially rectangular hollow vertical cross-sectional areas may be filled with a secondary material, such as structural foam for improved structural integrity.
The present invention also provides for partial reinforcement of a plastic pallet by affixing sheet strips along relatively weak structural portions of the pallet to form a plurality of substantially rectangular hollow vertical cross-sections along the length of the relatively weak structural portions for improved stiffness without loss of impact strength.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings wherein like reference numerals correspond to like components.